Many different pumping systems and constructions are well known. Apart from piston pumps and centrifugal pumps there are various rotary piston pumps which seek to combine the advantages of the piston pump and the centrifugal pump. However, in practice many difficulties are encountered. These difficulties relate, in particular, to control of the vanes.
The design according to U.S. Pat. Application No. 311,816, now U.S. Pat. No. 3,895,893, and other disclosures of the inventor provide, among other things, for eccentric control stubs, guided in cam tracks, on the bearing shafts of the vanes. Simple cam guides of this type, which are also common for other displacements, are sufficient for many applications. However the pump according to the present invention is also intended for use with media which are of especially high quality or for contaminated media, which in addition often contain relatively coarse constituents. An effort is therefore made to avoid corners and edges in the pump channel and, in particular, in the inlet and output areas as well, so that ramps in front of the entrance to the sealing portion of the channel should be avoided wherever possible. However there is then an increased danger of jamming if media containing coarse constituents are pumped. Since, for reasons of space, only small eccentricities, relative to the size of the vanes, can be employed at the ends of the control stubs, although an effort will be made to design them as large as possible, these control stubs will be subjected to considerable forces. Even constituents in the medium to be pumped which are not actually that hard can therefore easily lead to damage to or breakage of the control means and/or the vanes.